Neurological impairment, physical trauma, surgery or prolonged immobility frequently results in loss of range of motion due to contraction of the muscles, tendons and ligaments of the limbs or digits known collectively as “soft tissue”. Soft tissue contraction can result in loss of range of motion of the limb in flexion or extension. Rehabilitation efforts to reduce or stretch such contractions usually involve extensive physical therapy or surgical intervention. Both physical therapy and surgical alternatives frequently include the use of some form of orthopedic splint. Such orthopedic splints are available as adjustable “off-the-shelf” devices or hand crafted custom orthotics molded to fit the individual patient or specific application. Although some splints may include attributes of both, orthopedic splints generally fall into one of two general categories known as static or dynamic.
Static splints are primarily designed to hold the limb or digits at a preset position and may be manually adjustable to accommodate different limb or digit positions. Static splints may be adjustable to fit off-the-shelf products or custom fitted orthotics. Serial casting is a form of static splinting where a series of casts hold the limb or digits in a succession of positions. Static splints are commonly used to restore range of motion, prevent the occurrence of soft tissue contraction associated with long term immobilization, hold limbs in the desired post-surgical position during healing, or as a mechanical support for ambulating.
Dynamic splints use components, such as springs or elastic bands, in order to provide an active tension as the soft tissues stretch, in essence “taking up the slack.” As with static splints, dynamic splints may be off-the-shelf or custom made orthotics. Dynamic splints are designed to improve limb range of motion through exploiting the viscoelastic properties of soft tissues. When force is applied, soft tissues initially enter the elastic phase of stretch, a temporary condition wherein soft tissue returns to its previous state when force is removed. Under increased force or prolonged duration soft tissue enters the plastic phase of stretch where some permanent physical lengthening of the soft tissue is achieved. If the level of force or onset rate at which the force is applied is too great, soft tissue may be stressed beyond the intended plastic phase and may be torn or otherwise damaged. In order to achieve effective reduction of soft tissue contraction, it is imperative that a dynamic splint provide a precisely adjustable level of force that may be reliably reproduced and incrementally increased over successive therapy sessions. Of equal importance to the level of force applied is control of the direction and location at which force is applied. Misapplied force from a poorly designed or poorly fitting splint may force the limb outside the natural range of motion and de-stabilize the joint or cause permanent damage to the soft tissues.
Custom made orthotics are individually fabricated using molds taken from a patient's limb. Such orthotics generally offer superior fit and comfort through more uniform dispersion of pressure over the entire contact area of the splint. Such a custom fit may reduce some of the distortion problems found with off-the-shelf dynamic splints. Due to the labor intensive manufacturing process, custom orthotics are much more expensive than off-the-shelf splints and are not immediately available due to the extensive molding, manufacturing and fitting process required. Finally, custom orthotics are not easily adaptable and may require periodic replacement due to patient growth.
Generally, existing prior art is in the form of off-the-shelf splints. These pre-manufactured devices are often available in several standard sizes. Referring to FIG. 1, typically the rigid structural components 9 are fastened to a limb 10 via padding material 13 and 14, and a series of adjustable strap attachments 15 and 17. A variety of spring or elastic components are employed to provide force on the rigid structural components at a hinge point 19.
Referring to FIG. 2, the distortion of padding and strap attachments, when placed under stress S, result in twisting of the splint's strap attachments 15 and 17 at their intersections 12 and 14 with the rigid structural components 9. This twisting distortion allows the structural components 9 to shift from the desired alignment geometry, resulting in unintended joint stresses, and uneven distribution of pressure and constriction of the soft tissues of the limb 10.
Referring now to FIG. 3, the prior art structural components 9 and 9′ follow the medial and lateral contours of the limb 10. Prior art structural components located medial and lateral to the limb require several angular changes A and A′, for example, to conform to the contours of the limb 10. Prior art structural components are generally made of flat material with strength concentrated in a single vertical plane.
With reference now to FIG. 4, the flat structural components 9 and 9′, while under stress or tension, are located medial and lateral to the limb 10 and they tend to twist (T) out of the desired alignment. As the structural components 9 and 9′ (as well as 12 and 12′) roll out of the desired vertical alignment, overall structural integrity of the splint is compromised due to the resulting flexing of the structural components, and distortion of the load paths. Other prior art devices compensate for this rolling effect by using heavier and more expensive structures such as tubing that is square in cross section.